In recent years, fine particles in nanometer order are considered to be applied to various devices. For example, metal fine particles of nickel are currently used for a ceramic capacitor, and the use of fine particles having a particle size of 200 nanometer or less with good dispersibility is considered for a next-generation ceramic capacitor.
Additionally, fine particles of silicon monoxide (SiOx: x=1 to 1.6) with a lower oxygen content than silicon dioxide are utilized as a deposition material for an antireflective film of an optical lens or a gas barrier film for food packaging.
As common methods of producing fine particles in nanometer order, there are a method of introducing a bulk material as a raw material with beads of ceramic or zirconia and atomizing the material by mechanical pulverization, a method of melting and evaporating the material and spraying the material to air or water to obtain fine particles and methods for obtaining fine particles chemically such as electrolysis or reduction. Among them, a method of using thermal plasma (approximately 10000 C.°) such as high-frequency plasma or arc plasma to fabricate fine particles in a vapor phase is extremely useful from viewpoints that the dispersibility of the produced fine particles is excellent with reduced contamination, and that composite fine particles made of plural kinds of materials can be synthesized easily (for example, refer to JP-A-2002-45684 (Patent Document 1)).
FIG. 4 is a schematic cross-sectional view of an apparatus for producing fine particles using multi-arc plasma in a related-art example 1.
A plurality of bar-shaped electrodes 204 are circumferentially arranged on a ceiling portion of a reaction chamber 201, and respective electrodes 204 are arranged so that intervals therebetween are narrowed toward the center of the reaction chamber 201. The reaction chamber 201 is controlled to be a reductive atmosphere by introducing a gas. An AC power source 205 is connected to the respective electrodes 204, sequentially applying voltages having different phases to the respective electrodes 204 to thereby generate an arc discharge between the respective electrodes 204. A device for feeding a material as a raw material of fine particles and a material feeding piping part 211 are arranged in an upper part of the arc discharge. The material is fed to the arc discharge generated between the respective electrodes 204 from the material feeding piping part 211. The material fed from the material feeding piping part 211 is evaporated by the high-temperature arc discharge, reacting with a generated reactant (oxygen atoms, nitrogen atoms) and is rapidly cooled in a vapor phase, thereby generating fine particles of various kinds of compounds. In a lower side of the reaction chamber 201, a discharge port 226 discharging fine particles generated by the arc discharge and a ladle 227 temporarily reserving fine particles discharged from the discharge port 226 are provided.